Manufacture of sulfuric acid.



MANUFACTURE OF SULFURIG ACID.

APPLmAMoN HLBD SEPT. 10, 1909.

Patented DC.31,1912.

HNNQ ||||||||||||1|||||I UNITED sTATEs PATENT oEEIcE.

WILHELM FULDA, OE GRIESHEIM, GERMANY, ASSIGNOR T0 lCIEIEMISCH'E FABBIK GEIESHEIM-ELEKTRON, OF FRANKFORT-ON-THE-MAIN, GERMANY, IA CORPORA- TION OF GERMANY.

MANUFACTURE 0F SULF'URIC ACID.

Application led September 10, 1909. Serial No. 517,112.

To ali whom 'it may conce-rn:

Be it known that I, WILHELM FULDA, a subject of the German lEmperor, and resi,- dent of Griesheim-on-the-Main, Germany, have invented ci'tain new and useful Improveniente in the Manufacture of Sulfuric Acid, 'of which the following is a specification. v

In the manufacture of sulfuric acid by means of oxidizing agents in the form. of nitrosyl acid many proposals have vbeen made to replace the costly lead chambers by towers, but hitherto these proposals have not proved successful. According to Lunges statement (vide Lunges Handbuch der Sodcmlustre, III edition, vol. 1, page 1005), the processes hitherto proposed have the disadvantage that they require too great a consumption of-oxidizing agents. It has also been attempted to produce sulfuric acid by the use of nitric acid as an oxidizing agent, but this has not been successful, the losses of nitric acid being so high as to make the process practically unavailable, (m'de Muspratts T echm'sche Chem/ie, IV edition, vol. VII, page 1293).

The manner in which according to my invention the loss of combined nitrogen is avoided will hereinafter be explained. I Will only mention here the advantages of my new process over those hithertoA known. These advantages consist in that the new process requires less reaction space and a more concentrated acid is obtained. A cubic meter of reaction space furnishes from 100 1:0140 kilograms of acid of from 50 to 54 Baum, or evenO to 58 Baume, as against 5 to 7 kilograms of acid of 50C to 54 Baumein the case of lead chambers. In addition to this, the process according to this invention has the great advantage that it is not, (as is the case with the lead chamber and contact processes) confined to the use of a definite and uniform concentration of the SO2. gases, as the concentration can vary within 'wide limits, so that with the processaccording to this invention it is possible `to utilize sources of sulfurous acid which supply a current of gas of irregular composition. Such sources of SO2 are, for instance, certain ore roasting processes and other processes in which gases containing S02 are evolved. AFurther in the process in accord-,f

ance with this invention, it is possible to obtain acids of l greater concentration lthan those hitherto obtained in the lead chamber process and the nltric acid used as oxidizing agent can lbe recuperated as such, that is in the highest, and consequently most active, state of oxidation of nitrogen.

To successfully carry out the process ac# cording to this invention, it 1s necessary to observe a number of essential points, some oxidation into higher oxids and HNOS. A.

quantitative separation of the two reactions as regards both time and space is essential for if such separation is not effected the complete conversion of the nitric oxid into higher oxids is impossible owing to the -constant presencd of SU, and great losses of oxidizing agents occur. In the lead chamber process enormous spaces' are `required to avoid these losses. Further in order to obtain an acid of 58 Baume, care should be taken that an acid of about 56 to 58D Baume should flow down-through the oxidation towers C and D'. An acid with a higher Fconcentration than 58 has not proved practical as such acids can only`be fully deni trated with difficulty if only cold S()2 gases are available.

The necessity of a quantitative separation is pointed out here in an express manner for the first. time. Processes are indeed known (for instance, that disclosed in the specification of the British Patent, No. 972 A. D. 1871) in which separate apparatus are used for the oxidation, of the sulfurous acid and the regeneration of the nitric'acid. But it is in this specification nowhere mentioned that care should be taken that this separation actually takes"place,' although they economica]`. ,success q'f the tower process depends 'upothis separation. `This fact is explained by the low reaction power` possessed by di- Such specification of Letters Patent. Patented Dec, 31, 1912,

- of which have already been taken into con: i

`certained that special care should be taken lute cold gases which, when noquantitative t separation takes place, results in the production of NO down to the very end of the apparatus; thisNO not beingjcapable of bccoming completely oxidized is therefore lost.

The three special features which differentiate this invention from other tower processes are first the use of such a large. excess of nitric acid as oxidizing agent, second the separation of the process of formation' of sulfuric acid from the recuperation of the nitric acid and third that sulfuric acid of. from 5Go to 58o Baume is constantly sprayed into the oxidation towers C and D along` with the nitric acid.

lWe will now deal with the second reac tions, namely, the reconversion ofthe nit-ro-r gen oxids into nitric acid. As the reactions occurring in the conversion of the nitrogen oxids into HND, require much time for their completion, care must be taken that the gases remain a sufficiently long time in the apparatus, It has been found that for the perfect oxidation to nitric acid at least four minutes are required. Such a long time and correspondingly large space are necessary because the reactions in the highly diluted gases containing nitric oxid which are dealt with proceed at a very slow rate. A pyrites furnace containing a charge of 10,000 kilograms supplies, per minute, 40 cubic meters of gas. It has been found that the space required for the regeneration of the nitric acid should be equal to at least 4x40=160 cubic meters. Tn none 4of the tower processes hitherto known has this point been taken into consideration, Tt is further lanecessary to provide as large an absorption surface as possible for the absorbing liquid. Moreover, the temperature of this liquid should not be much above 30 centigrade. lt has been asto maintain as low a temperature as 300C. in the last 40 or `50 per cent.. of the absorption space. In none of the processes hitherto known was any value attached to the maintenance of this low temperature. 0n the contrary it was eren proposed to use warm water for the absorption.

It has been found that a most important factor for the perfect conversion of the nitrogen oxids into nitric acid is the amount of HNO, in the absorption liquid of the last parts of the apparatus; this amount should not be more than from 12 to 13 per cent. in the last Ll0 to 50 per cent. of the space, otherwise a considerable amount of nitrogen oxids will be lost.

The main points which are to be observed in the reconversion of nitrogen oxids into nitric acid are therefore: (l) each particle of gas should remain at least 4; minutes in the apparatus; (2) the absorption liquid, and consequently the gases, should be kept 'obtain the mixed acid of from as cold as possible, and (3) the HNOS con- Loaaeaa tents of the absorption liquid. in the last 40 or 50 per cent. of the absorption space should be below 13 per cent.

As already stated, the absorption liquid should present as large an absorbing* surface as possible The accompanying drawing illustrates, more or less diagrammatically, an apparatus adapted for carrying out the improved process.

ln the drawing the course of gasthrough the apparatus is indicated by a dotand-dash line, the path followed by the nitric acid and water is indicated by a solid line and the course of the sulfuric acid by a dotted line.

The sulfurous acidproduced by the action of a roasting kiln A is conducted through a Glover tower B having a cooler b and sprinkling devices b. From the tower B the gases are conducted through a tower, or towers, (or tower-like chamber, or cham bers) of any suitable construction, such as C, into which a spray, of a mixture of nitric acid of from 300 to 35o Baume and sulfuric acid of 56 to 58o Baume is sprayed in. This tower or these towers and the succeeding tower or towers need not necessarily be filled with material. They can if desired be empty and the liquids be injected by means of nozzles preferably arranged in the roof, or cover. ln the oxidation tower C or tow ers C and D the oxidation of the sulfurous acid to sulfuric acid takes place almost instantaneously. The mixture of nitric and sulfuric acids is thereby denitrated down to 1 per cent. and the concentration of the sulfuric acid of the mixture in the towers C and D is again raised to 56 to 58 Baume. This acid is pumped again partly into the oxidation towers and partly de-nitrated and concentrated in the Glover tower,'or other in a. special apparatus.

The gaseous nitric oxids liberated in the Glover tower B enter the tower C, or towers, into which nitric acid of from 25o to 30 Baume, or a mixture of nitricl and sulfuric acids, of from 25 to 300 Baume is sprayed. The proportions of nitric acid and' of sulfuric acid in this mixture are 95 lit-ers nitric acid and 5 liters sulfuric acid respectively and the degree of concentration of each of the acids, which is necessary to 25 t0 30o Baume is as follows: nitric acid 24 to 29 Baume, sulfuric acid 50'to 57 Baume. In the nitric acid tower, or towers El, the acid is raised to 30, or 350, Baume and then used in-- the oxidation towers C and D. Thereupon the gasesenter the tower E2 for the conversion of S02 into H2504. The space required for this part of the absorption apparatus is about 20 per cent. of the whole space. Thereupon the gases enter a tower D or towers into which nitric acid of from 10 to 25 Baume is sprayed whereby l the acid is enriched. .The space required here is about 30 per cent. of the whole space.

In the lremaining 50 per cent. of the total space the gases containing the nitric oXid come into intimate contact with an acid containing from 0 to 13 Aper cent. HNOS.

In the apparatus shown .in the drawing three sets or groups of towers, El, E2 and Ea are shown. F1, F2, F 3, Fg'and F5 indicate acid receptacles arranged below the level of the several towers and G`1, G2, G3, and G., are similar receptacles arranged at a higher level t-han said towers. A series of pressure tanks H1, H2, H-3 and H4 are connected with the lower series of receptacles F1 toF4 respectively'and a tank J into which sulfuric acid may be drawn is connected with the tank F5. The several groups of towers and the tanks are connected so that the acids and water will circulate through the apparatus in the manner indicated, a fan K being provided for drawing the gas through Athe several towers as represented bythev dot-'anddash line.

. It will be seen that wateriss rayed into the towers E3 and the mixture o waterl and i nitric acid is then circulated* through the towers E2, E1 and oxidizing towers G and D. Y In the actual practice of the invention it will be understood that it is necessary to cause the acld to circulate several times through the same tower in order-^to obtain the desired strength.

In order to maintainv the temperature of the absorption apparatus as low as possible, the absorption liquid circulating in the tower or towers is cooled. For the purpose of conversion into sulfuric acid of the sulfurous acid supplied by.a pyrites furnace taking a charge of 10,000 kilograms and producing 40 cubic meters of gas per minute,

A and for the purpose of converting` the nitrogen ozzids formed thereby'into nitric acid of from 309 to 3.5" Baume, only about 200 cubic meters space -1snecessary 1n accordance with 'the hereinbefore described process. Of

' these 200 cubic meters, about 30 cubic meters are needed for the oxidation of the sulfurous acid by the towers C and D, the remainder being utilized for' the regeneration of the nitric acid. 'The amount of space thus rej uired can be reduced by about 40 per cent.'

:50 per cent. of the regenerating space) if the last remnants of the nitrogen oxids be absorbed by sulfuric acid of at least 59 Baume, instead of by water. The nitric acid regenerating space still amounts to- 90 cubic meters, in which over 90 per cent. of the nitric acid used is recuperated as such. If more than 50 per cent. of the regeneration space be replaced by this mode of absorption by means of sulfuric'acid, it is no longer possible 'tooxidize theNO to suchan extent that 'it .will be fully taken up by the sulfuric acid. Besides this, the vrequired quantity of nitric acid is no longer obtained.'

The nitrisulfuric acid is freed from nitrogen oxid compounds in the Glover tower as aforesaid. The nitrogen oxids come ,again into the oxidation tower, or towers,and that, or those, for the formation of sulfuric acid.

Having thus described the invention, what is' claimed is:

1. The method of manufacturing sulfuric `v acid from sulfurous acid bymeans of nitric' acid, comprising the oxidation.` of the sulfurous acid and the regeneration of the nitric acid, the time and space of' the re-v name to this speciication inthe presence' of two subscribing witnesses.

Witnessesz' FRANZ Hassnacirmz, E RwIN DIPPEL. 

